This nonprovisional application claims priority under 35 U.S.C. xc2xa7 119(a) on Patent Application No. 2001-283694 filed in Japan on Sep. 18, 2001, which is herein incorporated by reference.
The present application claims priority under 35 USC 119 to Japanese Patent Application No. 2001-283694 filed on Sep. 18, 2001 the entire contents thereof is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a collision detecting apparatus for a vehicle, which outputs a collision signal for starting a passenger protector for a vehicle, such as an air bag upon collision of the vehicle.
2. Description of Background Art
With respect to the collision detecting apparatus to which the present invention pertains, as described in Japanese Patent Laid-open No. Hei 4-176757, there is known a type including an integrating means for cumulatively integrating the output from an acceleration sensor when the output exceeds a specific calculation start level due to collision of the vehicle, wherein the collision detecting apparatus outputs a collision signal when a cumulative integral value calculated by the integrating means exceeds a specific threshold value.
The output from the acceleration sensor (detected acceleration) is rapidly changed upon collision of the vehicle. The output, however, may be sometimes periodically vary due a variety of causes other than collision during the operation of the vehicle. In this case, if the cumulative integral value of the output from the acceleration sensor exceeds the threshold value, a collision signal is uselessly outputted from the collision detecting means despite a collision of the vehicle, which requires the operation of a passenger protector, that does not occur.
For example, a motorcycle includes an acceleration sensor often mounted to a leading end portion of a front fork and its neighborhood as shown in FIG. 4 (see Japanese Patent Laid-open No. Hei 11-278342). When a front wheel rides past a stepped portion, a series of motions are applied to the leading end portion of the front fork. First, a large deceleration is applied thereto due to the contact between the front wheel and the stepped portion. Second, a large deceleration is applied thereto due to compression and bottoming of a suspension spring for the front wheel. Third, an excitation force in the vertical and longitudinal directions due to, for example, release of the compression of the suspension spring is applied thereto when the front wheel is moved upwardly. At last, a large deceleration is applied thereto when the front wheel is grounded. These series of motions cause, for example, a resonance of the front fork. As a result, the output waveform from the acceleration sensor sometimes becomes a periodical damped vibration waveform as shown in a graph of FIG. 4. The vibration waveform is characterized in that an amplitude of each of the second and later wave crests (2), (3) . . . becomes larger than that of the first wave crest (1).
According to the related art collision detecting apparatus, as the amplitude of the vibration waveform of the output from the acceleration sensor becomes large (particularly, in the order of the second and later wave crests), a cumulative integral value of the output from the acceleration sensor may sometimes exceed the threshold value. In this case, an erroneous collision decision may be made (that is, a collision signal is erroneously outputted) despite any collision of the vehicle that does not occur, to thereby uselessly start a passenger protector.
In view of the foregoing, the present invention has been made. It is an object of the present invention to provide a collision detecting apparatus for a vehicle, which is capable of preventing the occurrence of an erroneous detection due to a periodical vibration of acceleration due to a cause other than a collision of the vehicle, thereby accurately performing a collision decision.
To achieve the above object, according to the present invention, there is provided a collision detecting apparatus for a vehicle including an acceleration sensor for detecting an acceleration upon collision of the vehicle, integrating means for cumulatively integrating an output from the acceleration sensor when the output exceeds a specific calculation start level, and collision detecting means for outputting a collision signal when a cumulative integral value calculated by the integrating means exceeds a threshold value. The collision detecting apparatus includes vibration waveform detecting means for detecting that an output waveform from the acceleration sensor is a specific periodical vibration waveform, and correcting means for correcting the threshold value on the basis of detection of the vibration waveform by the vibration waveform detecting means so as to lower a detecting sensitivity of the collision detecting means.
With this configuration, upon collision of the vehicle, a collision signal is outputted from the collision detecting means when a cumulative integral value calculated by the integrating means exceeds a threshold value. Meanwhile, when an output waveform from the acceleration sensor becomes a specific periodical vibration waveform as a result of a cause other than collision, for example, riding past a stepped portion, the threshold value is corrected on the basis of detection of the vibration waveform by the vibration waveform detecting means so as to lower a detection sensitivity of the collision detecting means. As a result, a collision decision is more carefully made, to prevent the collision detecting means from outputting an unnecessary collision signal due to the vibration waveform. This is advantageous in that even if a relatively large vibration of acceleration occurs due to a cause other than a collision, the collision decision can be accurately performed with a high responsiveness, so that a starting time of a passenger protector can be optimally controlled on the basis of the collision decision.
According the present invention, when after the output from the acceleration sensor exceeds the calculation start level and then returns to the same level and the output exceeds the same level again within a specific time, the vibration waveform detecting means decides that the output waveform is a vibration waveform and outputs a detection signal. With this configuration, the generation of a vibration of acceleration as a result of, for example, riding past a stepped portion can be simply, accurately detected.
According to the present invention, when after the output from the acceleration sensor exceeds the calculation start level and then returns to the same level and the output does not exceed again the same level within the specific time, if the threshold value has already been corrected, the corrected threshold value is returned to the original threshold value. With this configuration, the convergence of the vibration of acceleration taken as a cause of correcting the threshold value or the dissipation of noise can be accurately detected. Since the threshold value is returned to the original value after the convergence of the vibration of acceleration or the dissipation of noise is detected, the operation can be rapidly returned to the usual collision monitoring operation after the cause of correcting the threshold is eliminated.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.